This invention relates generally to methods of repairing and restoring turbine components such as vanes or blades, and more particularly to procedures which involve the restoration of the shroud portion of blades that have become damaged or worn.
Turbine blades are normally carried in the engine by a central hub, and are disposed essentially radially with respect to the axis thereof. The ribbed mounting base portions of the blades are received in corresponding slots in the hub, with the blade shrouds nesting against one another and being held in assembled relation by a suitable ring. During the operation of the engine there is a minute but continuous vibration of adjacent blades with respect to one another and with respect to the hub. This vibration gives rise to wear at the opposite edges of the shroud, in the vicinity of what is known as the Z-notches of the shroud, making necessary a replacement of the blades in the turbine after a certain period of operation has elapsed.
In the past, the repair of blades has been undertaken by applying beads of welding material to those areas of a blade which have worn away. The material was generally applied with welding rod having substantially the same composition as that of the base metal of which the blade was constituted. The welded areas were built-up to a dimension exceeding that of the original part, and thereafter the excess removed by grinding, to thereby restore the part to its original geometry. Such procedures have already been used extensively in the restoration of blades, and have met with a high degree of success.
However, as outlined above the prior procedures have several disadvantages. The welding rod employed tended to be expensive, running in excess of $100 per pound at current prices. In addition, since the welding had to be accomplished by hand, there were additional costs involved with labor. Moreover, because the blades were to be exposed to high temperatures and stresses in use, there was required a number of inspections during the processing in order to be sure that the welds were adequate, and to be sure that a satisfactory bond was obtained. Following this, the part was of necessity ground down to restore it to the dimensions of a new part. After the grinding, there usually were additional inspection steps that were required.
The costs involved with the above procedures were substantial, although they were generally less than those resulting from merely discarding old or worn blades and replacing them with brand new units.